Journal of the Ceramic Society of Japan
Online ISSN : 1348-6535
Print ISSN : 1882-0743
Feature: Cutting edge researches on electroceramics, 2015: Full papers
Solid state epitaxy of (Hf,Zr)O2 thin films with orthorhombic phase
Takanori KIGUCHIShogo NAKAMURAAkihiro AKAMATakahisa SHIRAISHIToyohiko J. KONNO
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124 巻 (2016) 6 号 p. 689-693

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Hf0.5Zr0.5O2 (HZO) thin films with orthorhombic phase Pca21 are novel ferroelectric materials. We have attempted the epitaxial growth of HZO thin films using solid-state epitaxy with ion-beam sputtering followed by rapid thermal annealing. X-ray diffraction (XRD) profiles of HZO thin films on SiO2 glass substrates showed {111}-oriented monoclinic and orthorhombic phases. On the other hand, XRD profiles of HZO on yttria stabilized zirconia (YSZ) (100) substrates indicated the shoulder peak on the strong tail of 200 peak of YSZ substrates in the lower 2θ side. Structural analyses of the HZO thin films have conducted to identify constituent phases, the local orientation, and the nanostructure of HZO thin films using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and the related STEM-EDS analysis. In this paper, we have described the orthorhombic (Pca21) and monoclinic (P21/c) phases coexisted based on multislice image simulation and diffractogram analysis of the local regions in HZO thin films. The principal phase in the HZO/YSZ epitaxial thin films is the orthorhombic phase. Each phase was epitaxially grown on the YSZ substrate with a domain structure of the order of 10 nm in size. The orthorhombic phase has formed in the HZO/SiO2 glass thin films, which indicates that the stability of the orthorhombic phase is ascribed to not only pseudomorphic or lattice mismatch effects of the substrate but also doping effects and thermal mismatch between the film and the substrate. The mosaicity of thin film is high because of lattice deformation with coexisting monoclinic phase and a damaged region between thin film and substrate caused by sputtered particles with high energy. Orthorhombic single-phase thin films with higher quality can be obtained by preparing ultrathin HZO epitaxial thin films under lower Ar-ion beam energy in the sputtering process and the higher crystallization temperature in the post-annealing process.

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